feat(properties): add parent_id for sub-property hierarchy

Phase 1 of the parent/child rollup feature. Self-FK on properties
with ON DELETE RESTRICT, plus a CHECK that blocks self-reference at
the DB level. Service-layer helpers (getDescendantIds,
getAncestorIds, assertNoCycle) walk the tree via recursive CTEs and
guard against cycles and cross-company parents. softDeleteProperty
now refuses to delete a property with live children.

No UI yet — readers and roll-up routes land in Phase 2.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

drizzle/0017_property_parent_check.sql

@@ -0,0 +1,7 @@
+-- A property cannot be its own parent. Deeper cycle prevention (e.g.
+-- A→B→A) is enforced in the service layer because Postgres can't express
+-- recursive CHECK constraints; the assertNoCycle helper in
+-- src/lib/server/services/properties.ts walks ancestors before save.
+ALTER TABLE "properties"
+  ADD CONSTRAINT "properties_parent_not_self"
+  CHECK (parent_id IS NULL OR parent_id <> id);